"It is supplying air at a constant rate" means number of moles only dude. And if increase in number of moles is constant, increase in volume is not, because pressure inside is dropping you see, so same number of moles will occupy more volume after some time.

Consider it this way
we can assume that constant rate of air flow means constant force due to change in momentum of the entering gas due to difference in force the radius start inc after forces equal radius becomes constant so it's c

bro in option B initial pressure is high and final is low which cant be possible when constant flow is present

@vishwas_gupta@Chirag_Hegde
I think what we did yesterday isnt completely correct.
Maybe the set up is like this. There is a thin flat film of liquid and the pump is blowing air on the film. Somewhat similar to what we do in those bubble making toys.
If you see,
At t = 0, R \rightarrow \infty
So P \rightarrow 0
Also,
We cant continuously keep filling in air, the film will either rupture or a bubble is formed. We don't need to consider the first case as its given that bubbles are being formed. So after a certain time, the bubble is formed and it will detach, and it will have a constant radius.
Hence.P = \text{Constant}